PROJECT SUMMARY The human lung is vast organ with exquisite regional differences in the form of cellular niches best defined at single-cell resolution. Emerging evidence led to growing appreciation that the collective roles of these fine specializations are fundamental for lung function. Guided by the scientific premise that these niches are often sites of pathogenesis, we propose to map these niches in normal and disease tissues and directly compare them at the single-cell resolution. This goal is directly responsive to the mission of LungMap Phase 2 to ?extend to more specific and rare cell types.? To achieve this goal, we have gathered an interdisciplinary team of established and rising, basic and clinical investigators with complementary strengths in developmental biology (Sun), cell biology and immunology (Prince, Sajti), technology development and informatics (Ren, Preissl, Wang and Xu). Together, we have a track record of studying the control of normal lung maturation, as well as mechanisms underlying a number of LungMap-highlighted diseases, including bronchopulmonary dysplasia, congenital diaphragmatic hernia, childhood interstitial lung disease, and pediatric pulmonary hypertension (PPH). We will use cutting-edge technologies such as single-nucleus ATACseq, single-cell and single-nucleus RNAseq, multiplex antibody and RNA in situ hybridization, and three-dimensional imaging. Using these, we will systematically define the exciting kaleidoscope of cell types in the human lung, with an emphasis on cellular niches that are central to pathogenesis.